A discrete device such as a metal-oxide semiconductor (MOS) transistor is widely employed as a switching device of a semiconductor device. Accordingly, fabrication of high performance MOS transistors is required in order to improve characteristics of the semiconductor devices. In order to achieve fabrication of high performance MOS transistors, research into ways of applying a physical stress to the channel region to improve the mobility of carriers is underway.
In general, the mobility of holes can be improved by applying a compressive stress to a transistor channel region in a case of a PMOS transistor, and the mobility of electrons can be improved by applying tensile stress to a transistor channel region in a case of an NMOS transistor. Accordingly, in producing complementary sets of metal-oxide-semiconductor (CMOS) field effect transistors, a compressive stress film and a tensile stress film are independently formed in PMOS and NMOS transistors, respectively. In such a case, separate masks for shielding each transistor region are required, and the fabrication processes may become complicated. To simplify the fabrication process without using separate masks, a tensile stress film may be formed on the PMOS transistor. However, the characteristics of a PMOS transistor including a SiGe channel region, specifically, on-current characteristics, may degrade.